changed v8 version to  commit 21d700eedcdd6570eff22ece724b63a5eefe78cb
moved build to mono 3.10
Fix portability issue with sgen garbage collector

While the Bohem garbage collector works with V8.Net sgen has an issue
with the statement InternalHandle.cs:111 and InternalHandle.cs:119 in
order to fix this we needed to store InPtr's instead of HandleProxy*
pointers.

Also we needed change the test to make them pass on a x64 bit system.